Portable battery pack



FIG. 1 is a perspective view of a portable battery pack according to the present design;

FIG. 2 is a rear elevation view of a portable battery pack according to the present design;

FIG. 3 is a top elevation view of a portable battery pack according to the present design;

FIG. 4 is a front elevation view of a portable battery according to the present design;

FIG. 5 is a bottom elevation view of a portable battery pack according to the present design; and,

FIG. 6 is a side elevation view of a portable battery pack according to the present design. 

The ornamental design for a portable battery pack, as shown and described. 